In recent years, in order to minimise the emission of noxious gases to the environment, a series of technologies has been incorporated into internal combustion engines. The reduction of emissions of these gases is connected, amongst other factors, with an increase in the thermal output of the internal combustion engine, and consequently the reduction of specific fuel consumption.
As a consequence, new engines have gone through a process of “downsizing”, which consists in reducing their volume and weight, maintaining or increasing their specific power. This involves greater thermal and mechanical loads on all the components, which is further accentuated in the case of moving components, because of the wear and attrition present.
One of the components most subject to the forces generated by internal combustion engines is the connecting rod, which forms the link between the piston and the crankshaft in order to transform the linear movement of the piston into rotational movement. In this way, the connecting rod is, one the one hand, attached to the piston, and, on the other hand, attached to the crankshaft. According to this descriptive report, the end of the connecting rod attached to the piston is known as the top end, and the end of the connecting rod attached to the crankshaft is known as the bottom end.
At the bottom end, between the connecting rod and the crankshaft, a bearing is used made of a softer material in order to reduce the attrition and wear between the components. At the top end of the connecting rod, a bush is fitted between the eye and pin of the piston, also in order to reduce the attrition between the components. The bearings used on the connecting rods also has the function of allowing for easy assembly, withstanding misalignments in assembly and the shaft and accommodating particulates, as is well known to the technicians in this field. Although the example mentioned here makes reference to the bearings fitted to the connecting rods, it is true that bearings can be used on other components of a combustion engine, such as the crankshaft and the camshaft.
The bearings for these applications usually consist of a layer of carbon steel coated on their internal diameter with an alloy based on Pb and Sn (known as Babbitts or White Metal) or based on Al associated with Sn in different concentrations, or even of copper alloys containing different concentrations of Pb. These bearings made of copper alloys also have an additional coating based on Pb and Sn.
However, as mentioned above, the conditions of operation of internal combustion engines are becoming increasingly severe, and bearings made of alloys based on Pb and Sn, and those based on Al, collapse and do not guarantee the reliability and durability required. Therefore, in other words, current technologies are not sufficient to meet the demands of new engines, including tri-metallic bearings based on bronze (copper alloys).
To this must also be added the fact that the use of Pb has been strongly discouraged, and, in some countries, banned, bearing in mind the environmental risks associated with this element.
Other solutions to obtain a bearing free of Pb can be found in technical state documents U.S. Pat. No. 6,357,919 and GB 2,321,468.
Document GB 2,321,468 refers to a bearing that contains: a layer of metal; a layer of Cu alloy laid over the metal layer; an intermediate layer of Cu—Zn laid over the layer of Cu alloy and containing 20 to 50% Zn by weight; and an anti-friction layer based on Sn or Al laid over the intermediate layer.
In this document, the anti-friction layer may contain, amongst other elements, 0.1 to 25% Zn by weight, which leads to a lower fraction by volume of Zn precipitates and lower hardness. Apart from this, it is worth noting that the intermediated Cu—Zn layer displays lower resistance to seizing up as it does not contain a solid lubricating element and is characterised as a high hardness metallic layer.
Furthermore, document U.S. Pat. No. 6,357,919 describes a bearing containing: a layer of metal; an intermediate layer laid over the metal layer; and an anti-friction layer laid over the intermediate layer. This anti-friction layer is free of Pb, and is made of an alloy based on Sn, which contains between 2 and 10% Ag by weight. This Sn-based alloy may also contain between 0.1 and 25% by weight of one or more elements from amongst Cu, Sb, Zn and Ni.
However, this North American document does not put forward a solution that is advantageous from the economic point of view, as it uses precious metals, such as Ag, which increases the price of the bearing too much. Apart from this, it is worth remembering that silver is also disadvantageous from the point of view of electrochemical potential suitable for the higher rates of deposition using the electrochemical method.
Therefore, it will be noted that in the current state of the art, bearings display innumerable disadvantages, particularly regarding aspects such as load capacity, resistance to seizing up, resistance to wear, the use of high cost materials, or even the use of materials harmful to the environment.
However, in order to solve the problems given as examples here, and other problems encountered in the current state of the art, this invention has as one of its aims, that of providing a bearing that does not use materials or elements harmful to the environment, such as lead.
Another of the objectives of this invention is to provide a bearing with a greater load capacity in relation to bearings in the current state of the art.
It is also one of the objectives of this invention to provide a bearing that uses low cost materials in order to make producing it less burdensome.
Additionally, it is one of the objectives of this invention to provide a bearing that displays higher resistance to wear and to seizing up.
Because of its inherent characteristics, this invention may also solve other problems in the current state of the art not put forward here as examples, as the role discussed here of bearings and their problems is more by way of an example than exhaustive.